In modern "enterprise" computing environments, that is, computer systems for use in an office environment in a company, a number of personal computers, workstations, mini-computers and mainframe computers, along with other devices such as large mass storage subsystems, network printers and interfaces to the public telephony system, may be interconnected to provide an integrated environment in which information may be shared among users in the company. Typically, users may be performing a variety of operations, including order receipt, manufacturing, shipping, billing, inventory control, and other operations, in which sharing of data on a real-time basis may provide a significant advantage over, for example, maintaining separate records and attempting to later reconcile them. The users may operate on their own data, which they may maintain on the computers they are using, or alternatively they may share data through the large mass storage subsystems.
One such large mass storage subsystem is described in, for example, U.S. Pat. No. 5,206,939, entitled System And Method For Disk Mapping And Data Retrieval, issued Apr. 27, 1993 to Moshe Yanai, et al (hereinafter, "the '939 patent"), and U.S. patent application Ser. No. 07/893,509 filed Jun. 4, 1995, in the name of Moshe Yanai, et al., entitled "System And Method For Dynamically Controlling Cache Management," both of which are assigned to the assignee of the present invention and incorporated herein by reference. That patent and those applications generally describe an arrangement which allows data, as used by computers, organized in records, with each record being in well-known "CKD" ("count-key-data") format, to be stored in storage devices which provide a "fixed block" storage architecture. In this arrangement, a large cache is used to buffer data that is transferred from the storage devices for use by the respective computers, and, if the data has been modified, transferred back from to the storage devices for storage.
In the systems described in the aforementioned patent and patent applications, a directory table is used to provide information concerning the data that is stored in the mass storage subsystem. In one embodiment, in which the mass storage subsystem stores data on a number disk storage devices, the table includes information concerning selected characteristics of each of the CKD records stored in the mass storage subsystem, organized by device, cylinder and read/write head or track, and includes such information as record size and certain formatting characteristics. The amount of data that can be stored by individual storage devices is continually increasing over time, both in terms of the number of cylinders that each device can store and in the amount of data each track can store, and so the amount of information which such tables needs to store can become quite large. U.S. patent application Ser. No. 08/790,642, filed: Jan. 29, 1997, in the name of Natan Vishlitzky, and entitled "Digital Data Storage Subsystem Including Directory For Efficiently Providing Formatting Information For Stored Records," assigned to the assignee of the present invention and incorporated herein by reference, describes a directory table in which the amount of information required for the various records can be advantageously reduced; however, it would be helpful to further reduce the size of the directory table.